1. Field of the Invention
The present invention generally relates to a magnetic disk device, particularly to a magneto-resistive effect type head, used for writing/reading information to a recording medium in a magnetic disk device used as an external memory for a computer or the like.
Recently, since the recording density in a magnetic disk device has been more and more increased, a gap between the head and the recording medium has been drastically minimized. Therefore, the demand for high performance and high reliability heads, which are operable with a low flying area or a small contact area, has increased.
2. Description of the Related Art
FIGS. 1 and 2 illustrate one example of a known magneto-resistive effect type head used in a magnetic disk drive. FIG. 1 is a perspective view of a slider member of the magneto-resistive effect type head, and FIG. 2 is an enlarged sectional view taken along a line II--II in FIG. 1. In the illustrated head, the slider member 1, made of ceramic material such as Al.sub.2 O.sub.3 TiC or the like, has a pair of rails 3a, 3b on a surface thereof opposite to a recording medium (not shown), the rails 3a, 3b extend generally parallel to each other from a leading side to a trailing side as seen in a moving direction of the recording medium. A head element 2 is provided on the trailing side of one of the two rails 3a, 3b.
As shown in FIG. 2, the head element 2 is located on the trailing side and includes an insulation layer 4 such as Al.sub.2 O.sub.3 or other and similar material is also covered with a protection layer 5 of an insulating material such as Al.sub.2 O.sub.3 or other similar material. The head element 2 includes a reading section R wherein a magneto-resistive effect element 2a is nipped in a gap portion 9 of an insulating material interposed between a pair of a lower shield layer 7 and an upper shield layer 8 of NiFe or other similar material, and a recording or writing section W including a recording coil 10 and a recording magnetic pole (upper pole) 11. The upper shield layer 8 is used for both the reading section R and the writing section W. The magneto-resistive effect type element 2a is typically a multilayered structure including a magneto-resistive layer, a bias layer, and a magneto-control layer among others, which layers are depicted as a single layer in FIG. 2, for the sake of simplicity.
The magneto-resistive effect type element 2a detects the variation of resistance in the element caused by the magnetic field of the recording medium (not shown), and therefore, if there are any projections or foreign matter on the recording medium, there is a risk of collision therewith of part of the head element 2 on the slider member 1. If such a collision occurs, the resistance in the element increases due to the heat generation caused by the collision energy or a by friction, which in turn induces the variation of a base line of reproduction signals and is detected as the output variation. This phenomenon is called "thermal asperity" and a typical wave shape of this phenomenon is illustrated in FIG. 3. As is apparent from FIG. 3, the base line of the reproduction signals largely varies due to a rapid temperature rise in the element. As the flying height of the slider member 1 is reduced, the probability of collision of the slider member with the projections or foreign matter on the recording medium increases. Thereby, to realize high-density recording, it is important to suppress the probability of such a collision. In this regard, thermal asperity is discussed, for example, in "Magneto-Resistive Head Thermal Asperity Digital Compensation"; R. L. Galbraith; G. J. Kerwin; J. M. Poss; IEEE Trans on Mag., Vol 28, No. 5, 1992.